linux-kernel - Re: [PATCH -mm v2.2] mm: get rid of __GFP

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Message-Id: <20140410163831.c76596b0f8d0bef39a42c63f@linux-foundation.org>
Date:	Thu, 10 Apr 2014 16:38:31 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<devel@...nvz.org>, Greg Thelen <gthelen@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Glauber Costa <glommer@...il.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: [PATCH -mm v2.2] mm: get rid of __GFP_KMEMCG

On Thu, 3 Apr 2014 19:05:59 +0400 Vladimir Davydov <vdavydov@...allels.com> wrote:

> Currently to allocate a page that should be charged to kmemcg (e.g.
> threadinfo), we pass __GFP_KMEMCG flag to the page allocator. The page
> allocated is then to be freed by free_memcg_kmem_pages. Apart from
> looking asymmetrical, this also requires intrusion to the general
> allocation path. So let's introduce separate functions that will
> alloc/free pages charged to kmemcg.
> 
> The new functions are called alloc_kmem_pages and free_kmem_pages. They
> should be used when the caller actually would like to use kmalloc, but
> has to fall back to the page allocator for the allocation is large. They
> only differ from alloc_pages and free_pages in that besides allocating
> or freeing pages they also charge them to the kmem resource counter of
> the current memory cgroup.
> 
> ...
>
> +void *kmalloc_order(size_t size, gfp_t flags, unsigned int order)
> +{
> +	void *ret;
> +	struct page *page;
> +
> +	flags |= __GFP_COMP;
> +	page = alloc_kmem_pages(flags, order);
> +	ret = page ? page_address(page) : NULL;
> +	kmemleak_alloc(ret, size, 1, flags);
> +	return ret;
> +}

While we're in there it wouldn't hurt to document this: why it exists,
what it does, etc.  And why it sets __GFP_COMP.

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